This proposal deals with the role of lysosomes in the degradation of rod outer segment material that is phagocytized by the retinal pigment epithelial cells. First, problems regarding the identification and the morphological and enzymatic heterogeneity of lysosomes will be investigated by electron microscopic cytochemistry. They include study of the biogenesis of lysosomal dense bodies from organelles such as the Golgi apparatus or the specialized, acid phosphatase rich region of endoplasmic reticulum known as GERL (Golgi apparatus, endoplasmic reticulum, lysosomes). Cytochemically demonstrable acid hydrolase or other enzyme activities will be used as "markers" for these organelles. Also included is the identification of aryl sulfatase-positive bodies previously described in these cells and the search for lysosomes in C57 black mice which reportedly lack lysosomal dense bodies. The second part deals with the question of phagosome-lysosome interactions that lead to intracellular digestion of rod outer segments. It is proposed to label isolated rod outer segments with appropriate "markers" such as colloidal iron, cationized ferritin or lectin-ferritin conjugates, either by direct exposure or by intravitreal injection. The labeled rod outer segment preparations will then be added to explant cultures of retinal pigment epithelium. The study will include two types of experiments: 1) explant cultures will be exposed once to labeled outer segments and the progress of intracellular degradation followed by electron microscopy and 2) explants will be exposed to rod outer segments labeled with one marker, allowed to partially degrade the material and subsequently exposed to preparations labeled with another marker so as to follow interactions between pre-existing phagolysosomes and newly phagocytized rod outer segments. The last part of the proposal deals with the morphological and cytochemical study of lipofuscin formation in vitamin E deficient rats. These experiments are aimed at learning more about the transformation of rod outer segments into lipofuscin granules and their relations to lysosomes.